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LMZM23601: Short peak overload currents

Nikolai Orlov
Intellectual 290 points
Part Number: LMZM23601
Other Parts Discussed in Thread: LMZ34202

Hello,

Can I drive short (~ 100us) load current pulses higher than 1A max output current? I would expect about 1.2A to 1.3A peak current.

Will LMZM23601 operate in current limiting (1A) mode in this case and peak currents will be handled by the output capacitor. If 5V output LMZM23601 connected to 4 Ohm load will it operate in current source (current limit mode) and drive 4 Ohm resistor with 1A current?

Thank you!

  • 0
    TI__Mastermind 47060 points

    Hi Nikolai,

    The LMZM23601 will operate in current limit mode if more than 1A is pulled on the load. During this over current condition the device will enter hiccup mode where output voltage shuts down to prevent damage to the MOSFET and internal circuitry. This can be observed in Section 8.3.5. Because of this I don't think you can pulse short bursts of load current greater than 1A. 

    Regards,

    Jimmy 

  • 0 in reply to Jimmy Hua
    Intellectual 290 points
    Hi Jimmy,

    According to datasheet Page-26, Fig-39 during startup it works in current limiting mode, so with significant output capacitance (let's say 150uF) can I draw very short (less than 100uS) 1.3A pulses? Will it just go for 1A current limiting mode for the short period in this case?
    What is the over-current output threshold?

    Thank you,
    Nikolai
  • 0 in reply to Nikolai Orlov
    TI__Mastermind 47060 points

    Hi Nikolai,

    What is your initial condition (VIN , VOUT)? I looked further into this and did some calculations to see if the short 1.3A pulses might trip any fault in the device. Using this app note to calculate the maximum output current based on the valley current limit and typical values, I get the following: 

    Iout max = Ivalley + 1/2 ( Vin-Vout / Fs*L) * Vout/Vin

      • Ivalley = low side current limit = 1.2A (typ)
      • Vin = 24V
      • Vout = 5V
      • Fs = 1MHz
      • L = 10uH (fixed) 

    Iout max = 1.4A

    Though I still do not recommend going over the 1A rated current limit of the device, theoretically you can push higher currents through the device so long as the inductor valley current is below the Ivalley threshold. Since you are doing a short pulse of 100us or less at 1.3A I don’t think there is enough energy that would cause a fault issue. Because of this reasoning on startup condition, I think the 1.3A pulse will result in something similar to the current limiting you see in Figure 39 as you've mentioned. However I do suggest you test this out on your circuit and check for fault stability.

    Regards,

    Jimmy

  • 0 in reply to Jimmy Hua
    Intellectual 290 points

    Thank you Jimmy,

    Considering everything I've decided to use LMZ34202 which is designed to provide up to 2A current.

    Nikolai